Ease of setup is essential, but I also want to look at overall cost, reliability and fault tolerance. A controller per miner ensures no one box can affect the operation of another, but also has the highest cost.  A single controller for a fleet of miners is the cheapest and easiest to configure, but also provides a nice single point of failure. A single controller with chained boxes means if you pull any one cable, every miner downstream is also disconnected. Using a single controller with a tree structure of connected boxes reduces (but does not remove) this problem, and still leaves you with the controller as a single point of control but also failure.

I like the idea of the single controller being something generic and replaceable like the Pi. If your Avalon6 controller craps out, you don't have to email warranty claims and wait a week for them to deny your claim. Just go to any of a thousand online vendors and pick up a new one for like $20 - or if you're that worried about it, already have one standing by just in case. Avalon sending a Pi with the SD card already imaged is really nice.

The easiest busses for consumers to work with, as far as setting up a tree of connections using readily available hardware is concerned, would be Ethernet and USB. I'm in favor of USB from the standpoint of ease of interface (you can get $2 microcontrollers with full USB capability) and availability of software to build upon, but Ethernet does make distribution easier what with better cabling and generally more reliable hardware. The problem with ethernet comes from controlling it - either the miners have to be on a private network and a dual-NIC controller is present, or the miners exist on the same network which adds work to detection and preventing control overlaps.

Oh yeah, I was ecstatic when the S5s started showing up with DHCP enabled by default. Very glad to see that change. My entire hosting is run off static leases on the DHCP server, makes everything super easy.